U.S. patent application number 10/790111 was filed with the patent office on 2004-12-02 for method of producing a glass substrate for a magnetic disk and method of producing a magnetic disk.
This patent application is currently assigned to HOYA CORPORATION. Invention is credited to Tanaka, Hirotaka, Tawara, Yoshihiro.
Application Number | 20040238002 10/790111 |
Document ID | / |
Family ID | 33447008 |
Filed Date | 2004-12-02 |
United States Patent
Application |
20040238002 |
Kind Code |
A1 |
Tanaka, Hirotaka ; et
al. |
December 2, 2004 |
Method of producing a glass substrate for a magnetic disk and
method of producing a magnetic disk
Abstract
In a method of producing a glass substrate for a magnetic disk,
a principal surface of a glass substrate is subjected to polishing
in order to impart a texture thereon. Thereafter, a treating liquid
is supplied onto the principal surface of the glass substrate.
While a tape is pressed against the principal surface of the glass
substrate, the principal surface is cleaned.
Inventors: |
Tanaka, Hirotaka;
(Nirasaki-shi, JP) ; Tawara, Yoshihiro;
(Yokohama-shi, JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W.
SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
HOYA CORPORATION
|
Family ID: |
33447008 |
Appl. No.: |
10/790111 |
Filed: |
March 2, 2004 |
Current U.S.
Class: |
134/6 ;
G9B/5.299 |
Current CPC
Class: |
G11B 5/8404
20130101 |
Class at
Publication: |
134/006 |
International
Class: |
B08B 007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 3, 2003 |
JP |
56274/2003 |
Claims
What is claimed is:
1. A method of producing a glass substrate for a magnetic disk,
comprising: polishing a principal surface of a glass substrate to
impart a texture thereon; thereafter supplying a treating liquid
onto the principal surface of the glass substrate; and pressing a
tape against the principal surface of the glass substrate and
moving the glass substrate and the tape relative to each other to
clean the principal surface.
2. A method of producing a glass substrate for a magnetic disk
according to claim 1, wherein the treating liquid is pure
water.
3. A method of producing a glass substrate for a magnetic disk
according to claim 1, wherein the treating liquid contains
colloidal particles.
4. A method of producing a glass substrate for a magnetic disk
according to claim 1, wherein the tape for cleaning the principal
surface of the glass substrate has small foaming pores at least on
a surface of the tape.
5. A method of producing a glass substrate for a magnetic disk
according to claim 1, wherein the glass substrate is a chemically
strengthened glass substrate.
6. A method of producing a magnetic disk, wherein at least a
magnetic layer is formed on a glass substrate for a magnetic disk
obtained by the method according to claim 1.
7. A method of producing a glass substrate for a magnetic disk
according to claim 1, wherein the glass substrate is used as a
magnetic disk for a load/unload system.
Description
[0001] This application claims priority to Japanese patent
application JP 2003-56274, the disclosure of which is incorporated
herein by reference.
BACKGROUND OF THE INVENTION
[0002] This invention relates to a method of producing a glass
substrate for a magnetic disk for use in a HDD (hard disk drive) or
the like.
[0003] At present, following the rapid development of the IT
industry, the information recording technology, in particular, the
magnetic recording technology is requested to achieve dramatic
technical innovation. For a magnetic disk to be loaded in a HDD or
the like, it is required to develop a technology capable of
achieving an information recording density of 40 Gbit/inch.sup.2 to
100 Gbit/inch.sup.2 or more in response to a demand for a higher
capacity.
[0004] The magnetic disk is required to be particularly excellent
in magnetic characteristic in a flying/traveling direction of a
magnetic head. To this end, there is known a technique of forming a
texture on a surface of a substrate for a magnetic disk to impart a
magnetic anisotropy to a magnetic layer, thereby improving the
magnetic characteristic as a magnetic recording medium to achieve a
higher recording density as described in, for example, Japanese
Patent Application Publication (JP-A) No. 2002-30275.
[0005] In the meanwhile, attention is recently drawn to a glass
substrate as a substrate for a magnetic disk, which is suitable for
a higher recording density. The glass substrate has a high rigidity
as compared with a metal substrate and is therefore suitable for an
increase in rotation speed of a magnetic disk apparatus. Further,
the glass substrate makes it easy to lower a flying height of a
magnetic head because a flat and smooth surface is obtained.
Therefore, the glass substrate is advantageous in an improvement of
a S/N ratio of a recording signal and an increase in recording
density.
[0006] However, in case where the texture is formed on the surface
of the glass substrate as described in the above-mentioned
publication and if a magnetic disk produced from the glass
substrate is mounted to the HDD, there is a problem of easy
occurrence of a head crash defect and a thermal asperity (TA)
defect. These defects (failures in the HDD) have a high tendency to
occur after lapse of some time after the HDD is brought into market
and installed in a PC (personal computer) or the like. Therefore,
occurrence of these defects will lead to significant downfall of
creditworthiness in the market. This inhibits wide spread of the
glass substrate for a magnetic disk, which is capable of achieving
a higher recording density.
SUMMARY OF THE INVENTION
[0007] Therefore, it is an object of this invention to provide a
glass substrate for a magnetic disk, which is capable of preventing
occurrence of a head crash defect and a thermal asperity defect
even if a texture is formed by polishing a surface of the glass
substrate by the use of a tape and which is suitable for a higher
recording density.
[0008] The present inventors investigated a reason for occurrence
of the head crash defect and the thermal asperity defect mentioned
above in case where a magnetic disk is produced by the use of a
disk substrate provided with a texture formed by polishing a
surface of a glass substrate with a tape and the magnetic disk is
mounted to an HDD. As a result, it has been found out that a small
amount of contamination is often adhered to a surface of a magnetic
head mounted to the HDD in which those defects have occurred.
[0009] In order to investigate a reason for production of the
contamination, a texture was formed on the surface of the glass
substrate by the use of a tape under various conditions. As a
result, it has been revealed that, in presence of specific
disturbance in texture profile on the surface of the glass
substrate, similar disturbance in texture profile will be caused on
a surface of the magnetic disk produced by the use of the glass
substrate, promoting the production of the contamination on the
magnetic head.
[0010] FIG. 3 shows an example of the texture profile formed on the
surface of the glass substrate. In FIG. 3, it is confirmed that a
single line or streak of texture is higher by several nanometers
than a surrounding texture profile. It has been found out that, if
such disturbance as shown in FIG. 3 is present in the texture
profile, contamination tends to be attached to the magnetic
head.
[0011] Even if small unevenness in height on the order of several
nanometers is present in the texture profile as shown in FIG. 3,
such unevenness is sufficiently smaller than the flying height of
the magnetic head and, therefore, has not been recognized as a
problem so far. However, as a result of study by the present
inventors, it has been found out that the head crash defect and the
thermal asperity defect may be caused through the production of
contamination on the magnetic head.
[0012] According to the study by the present inventors, the reason
why the disturbance in texture profile is caused on the glass
substrate is considered as follows.
[0013] Specifically, the glass substrate has a high hardness and is
hard as compared with a substrate having a metal surface.
Therefore, when the glass substrate is polished with a tape to form
a texture, the texture is often disturbed by biting of abrasive
grains or small foreign matters. Further, since the glass substrate
is an insulator, such biting is difficult to eliminate because of
an electrostatic force generated by friction during polishing with
the tape. It is considered that the disturbance in texture profile
is caused by the above-mentioned reasons.
[0014] Based on a series of findings and considerations mentioned
above, the present inventors completed the invention having the
following aspects.
[0015] (First Aspect)
[0016] A method of producing a glass substrate for a magnetic disk,
comprising:
[0017] polishing a principal surface of a glass substrate to impart
a texture thereon;
[0018] thereafter supplying a treating liquid onto the principal
surface of the glass substrate; and
[0019] pressing a tape against the principal surface of the glass
substrate and moving the glass substrate and the tape relative to
each other to clean the principal surface.
[0020] (Second Aspect)
[0021] A method of producing a glass substrate for a magnetic disk
according to the first aspect, wherein the treating liquid is pure
water.
[0022] (Third Aspect)
[0023] A method of producing a glass substrate for a magnetic disk
according to the first aspect, wherein the treating liquid contains
colloidal particles.
[0024] (Fourth Aspect)
[0025] A method of producing a glass substrate for a magnetic disk
according to the first aspect, wherein the tape for cleaning the
principal surface of the glass substrate has small foaming pores at
least on its surface.
[0026] (Fifth Aspect)
[0027] A method of producing a glass substrate for a magnetic disk
according to the first aspect, wherein the glass substrate is a
chemically strengthened glass substrate.
[0028] (Sixth Aspect)
[0029] A magnetic disk is produced by forming at least a magnetic
layer on a glass substrate for a magnetic disk obtained by the
method according to the first aspect.
[0030] (Seventh Aspect)
[0031] In the method of producing a glass substrate for a magnetic
disk according to the first aspect, the glass substrate is used as
a magnetic disk for a load/unload system.
[0032] As set forth in the first aspect, a method of producing a
glass substrate for a magnetic disk according to this invention
includes polishing a principal surface of a glass substrate to
impart a texture thereon, thereafter supplying a treating liquid to
the principal surface of the glass substrate, and cleaning the
principal surface with a tape.
[0033] By the use of the tape as a cleaning member, it is possible
to remove abrasive grains or foreign matters adhered to the
principal surface of the substrate during the texturing step.
Simultaneously, disturbance of the texture formed on the surface of
the glass substrate is reduced by an appropriate pressing force
applied to the principal surface of the substrate during cleaning
with the tape. Further, by successively feeding the tape forward, a
pure cleaning member (tape) is continuously supplied onto the
principal surface of the substrate. Therefore, the foreign matters
and the like, which have once been removed by cleaning with the
tape, can not be adhered again. In the above-mentioned manner, a
uniform texture can be formed on the glass substrate.
[0034] As a cleaning method used in cleaning with the tape, which
is executed after the texture is formed on the principal surface of
the glass substrate, a single-substrate tape cleaning method is
preferably used. For example, such tape cleaning method may be a
rotary tape cleaning method. In the rotary tape cleaning method, a
specific tape is supplied onto and pressed against the surface of a
disk-shaped glass substrate which is rotating. Thus, the surface of
the glass substrate can be cleaned with high precision.
[0035] The tape used in the above-mentioned cleaning may be same as
a tape used in texturing. However, use of a different tape enables
a more uniform texture to be formed and is therefore preferable.
This is because, to the tape which has been used in texturing, a
slurry used in texturing and other foreign matters may be adhered.
Therefore, it is preferable to prepare a different tape, i.e., a
cleaning tape different from the tape for texturing and to carry
out cleaning with the tape.
[0036] Herein, a tape having a surface provided with very small
foaming pores is preferably used as the cleaning tape. In this
case, the cleaning tape may be a tape provided with very small
foaming pores formed on its surface or a tape provided with very
small foaming pores formed at least on its surface, with a core
member made of a different material. For example, a tape having a
surface comprising a foamed resin such as foamed polyurethane is
preferable because very small foaming pores are formed on the
surface and a function of uniformizing the texture during cleaning
with the tape is enhanced. Preferably, each foaming pore has a
diameter between 20 .mu.m and 100 .mu.m because a cleaning effect
during cleaning with the tape is increased and the function of
uniformizing the texture is enhanced.
[0037] In this invention, a treating liquid is supplied between the
tape and the glass substrate when the principal surface of the
glass substrate is cleaned with the tape. As the treating liquid,
for example, pure water is preferably used. By supplying the pure
water, it is possible to prevent adhesion of foreign matters during
cleaning so that a uniformly textured surface is formed. As the
pure water, use may be made of ultra pure water, such as RO water
(reverse osmosis water, RO: Reverse Osmosis) or DI water
(deionization water, DI: DeIonization). In particular, use of the
DI water subjected to deionization is preferable because
disturbance in morphology of a fine texture profile is
suppressed.
[0038] Preferably, the above-mentioned treating liquid in this
invention is adjusted to be neutral or alkaline. If adjusted to be
alkaline, a cleaning effect by a glass etching function is utilized
in combination. Therefore, as compared with the case where the
treating liquid is neutral, a higher cleaning effect is achieved.
However, in case where maintenance of morphology of the texture
profile is regarded important, it is preferable to adjust the
treating liquid to be neutral without the glass etching function.
Thus, it is preferable to adjust the treating liquid depending upon
the purposes, i.e., to adjust the treating liquid to be alkaline in
case where a higher cleaning effect is required even if the
morphology of the texture profile is slightly varied and to be
neutral in case where maintenance of the morphology of the texture
profile is desired although the cleaning effect is slightly
lowered. In order to adjust the treating liquid to be alkaline, a
chemical solution such as sodium hydroxide or potassium hydroxide
may be added. Specifically, the treating liquid is appropriately
adjusted so that PH falls within a range between 7 and 12.
[0039] In this invention, the treating liquid preferably contains
colloidal particles.
[0040] It is preferable to contain the colloidal particles because
it is possible to enhance a function of removing burrs of the glass
formed during texturing polishing and unevenness of the texture
illustrated in FIG. 3. Advantageously, it is also possible to
achieve a function of removing contamination such as an organic
substance adhered onto the glass substrate. The colloidal particles
preferably have a small particle size. For example, the colloidal
particles having an average particle size between 0.01 .mu.m and
0.5 .mu.m are preferably used.
[0041] As the colloidal particles, colloidal silica particles may
be used. The colloidal silica particles are particularly preferable
because the glass substrate can be highly purified.
[0042] In case where the colloidal silica particles are contained
in the treating liquid, the treating liquid is preferably adjusted
to be alkaline. By adjusting the treating liquid to be alkaline,
the above-mentioned advantageous function can be achieved.
Specifically, the treating liquid is preferably adjusted so that PH
falls within a range between 8 and 12.
[0043] In case where cleaning with the tape is carried out using
the treating liquid containing the colloidal particles, cleaning
with the tape may thereafter be carried out using a treating liquid
which does not contain the colloidal particles but comprises, for
example, pure water. In this event, it is possible to prevent the
colloidal particles from being left on the glass substrate.
[0044] In this invention, cleaning with the tape is advantageously
followed by scrub cleaning. By carrying out the scrub cleaning, it
is possible to more highly purify the surface of the glass
substrate. Further, it is possible to reliably prevent the
colloidal particles from being left on the glass substrate in case
where the treating liquid used in cleaning with the tape contains
the colloidal particles. In case where the scrub cleaning is
carried out, it is preferable to supply a neutral or an alkaline
cleaning liquid. Specifically, it is preferable to adjust the
cleaning liquid so that PH falls within a range between 7 and
12.
[0045] As a glass for the glass substrate in this invention, use
may be made of an aluminosilicate glass, a soda lime glass, or the
like. The aluminosilicate glass is preferable because a high
rigidity is obtained if it is treated into a chemically
strengthened glass.
[0046] Use may be made of an amorphous glass or a crystallized
glass comprising an amorphous component and a crystalline
component. If the amorphous glass is used, the function of this
invention is advantageously achieved.
[0047] The above-mentioned glass preferably comprises, as an
amorphous aluminosilicate glass, an aluminosilicate glass
containing 58-75 wt % SiO.sub.2, 5-23 wt % Al.sub.2O.sub.3, 3-10 wt
% Li.sub.2O, and 4-13 wt % Na.sub.2O as main components.
[0048] Further, the glass substrate preferably comprises an
aluminosilicate glass containing 62-75 wt % SiO.sub.2, 5-15 wt %
Al.sub.2O.sub.3, 4-10 wt % Li.sub.2O, 4-12 wt % Na.sub.2O, and
5.5-15 wt % ZrO.sub.2 as main components, with the weight ratio of
Na.sub.2O/ZrO.sub.2 being 0.5-2.0 and the weight ratio of
Al.sub.2O.sub.3/ZrO.sub.2 being 0.4-2.5.
[0049] In order to avoid occurrence of protrusions on the surface
of the glass substrate as a result of an undissolved portion of
ZrO.sub.2, use is preferably made of a chemically strengthenable
glass containing, by mol %, 57-74% SiO.sub.2, 0-2.8% ZnO.sub.2,
3-15wt % Al.sub.2O.sub.3, 7-16 wt % Li.sub.2O, and 4-14 wt %
Na.sub.2O.
[0050] By chemically strengthening, the above-mentioned
aluminosilicate glass is improved in transverse strength, increased
in depth of a compressive stress layer, and excellent in Knoop
hardness. A chemically strengthening method is not specifically
limited but may be any chemically strengthening method known in the
art. Practically, however, chemical strengthening by
low-temperature ion exchange is preferable.
[0051] In case where the above-mentioned chemically strengthened
glass substrate is used as the glass substrate, polishing for
imparting the texture is preferably carried out after a chemically
strengthening step. To form the texture before the chemically
strengthening step is not preferable because the texture profile
may be disturbed during ion exchange in the chemically
strengthening step. If the texture is imparted onto the glass
substrate after it is chemically strengthened and a compressive
stress is produced on its surface, a fine and elaborate texture is
obtained.
[0052] A diameter of the glass substrate is not particularly
limited. Practically, however, for a small-sized magnetic disk
which is not greater than a 2.5-inch magnetic disk and which is
often used as a mobile HDD, this invention is highly useful because
it is possible to provide a glass substrate for a magnetic disk,
which is high in shock resistance and which is capable of achieving
a higher recording density.
[0053] The glass substrate preferably has a thickness between 0.1
mm and 1.5 mm. In particular, in case of a magnetic disk comprising
a thin substrate having a thickness on the order of 0.1 mm to 0.9
mm, this invention is highly useful and advantageous because it is
possible to provide a glass substrate for a magnetic disk which is
high in shock resistance.
[0054] In the method of producing a glass substrate for a magnetic
disk according to this invention, a single-substrate tape texturing
method is preferably used in order to form a texture by polishing
with the tape.
[0055] As the single-substrate tape texturing method, a rotary tape
texturing method may be used for example. In the rotary tape
texturing method, a specific tape is fed onto and pressed against a
surface of a disk-shaped glass substrate which is rotating and a
polishing slurry such as a diamond slurry is supplied. Thus, a
circumferential texture, for example, is formed on the surface of
the glass substrate.
[0056] As an example of an apparatus for executing the rotary tape
texturing method, use may be made of a tape texturing apparatus as
illustrated in FIG. 1 (schematic diagram). The apparatus
illustrated in FIG. 1 is used in examples which will later be
described. In the tape texturing apparatus, a glass substrate 1
fixed to a spindle 101 is rotated and an abrasive is supplied
through a slurry (abrasive grains) dropping port 102 to tapes 103.
Opposite surfaces of the glass substrate 1 are clamped by the tapes
103 wound around rollers 104. Thus, a circumferential texture is
formed on each principal surface of the glass substrate 1. The
rollers 104 with the tapes 103 wound therearound are rotated at a
predetermined rotation speed so that a new surface of each tape 103
is continuously contacted with the glass substrate 1. In this case,
the spindle 101 can be wobbled. Plate-like members 105, 105 fixed
to shafts of the rollers 104 are moved around a support point a so
that the glass substrate 1 is clamped. At this time, a load applied
to the glass substrate 1 is determined by a force of a spring 106
extended between the plate-like members 105. The load is measured
by a tension meter 107.
[0057] By adjusting a substrate rotation speed (spindle rotation
speed) and a texturing time in this tape texturing apparatus, the
profile of the texture on the glass substrate can be adjusted.
[0058] A material and a shape of the tape used in texturing is not
particularly limited. A type of the tape may be a pile tape, a
woven fabric tape, a nonwoven fabric tape, or the like. As a
material of a tape fiber, use may be made of a plastic fiber such
as polyester and nylon.
[0059] As the polishing slurry supplied in polishing for imparting
the texture, a polishing slurry containing diamond abrasive grains
is preferably used. Among others, a polishing slurry containing
polycrystalline diamond abrasive grains is preferably used in view
of stable polishing and texturing. It is advantageous that the
diamond abrasive grains have an average particle size between 0.1
.mu.m and 1 .mu.m.
[0060] The texture in this invention is not specifically limited as
far as a magnetic anisotropy in a disk circumferential direction is
induced in a magnetic layer. For example, a circumferential
texture, a spiral texture, and a cross texture may be used. Among
others, the circumferential texture advantageously achieves the
effect of this invention because a direction of the texture is
similar to a traveling direction of a magnetic head flying and
traveling over a magnetic disk.
[0061] As regards a surface roughness of the texture, a flat and
smooth surface having Rmax of 5 nm or less and Rp of 3 nm or less
is preferable. Such flat and smooth surface defined by the
above-mentioned surface roughness contributes to a higher recording
density of the magnetic disk.
[0062] In this invention, Rmax represents a maximum height and Rp
represents a maximum peak height, both of which are defined in
Japanese Industrial Standard (JIS).
[0063] By forming at least a magnetic layer on the glass substrate
for a magnetic disk in this invention, a magnetic disk suitable for
a higher recording density is obtained. If a Co-based magnetic
layer having an hcp crystal structure is used as the magnetic
layer, a high coercive force (Hc) is obtained to contribute to a
higher recording density.
[0064] If necessary, an underlying layer is preferably formed
between the glass substrate and the magnetic layer in order to
control crystal grains of the magnetic layer and orientation
thereof.
[0065] Upon production of the magnetic disk, at least a magnetic
layer is preferably formed by DC magnetron sputtering using a
fixed-target deposition method.
[0066] The glass substrate for a magnetic disk according to this
invention is preferably used as a magnetic disk for a load/unload
system. In case where the glass substrate is used as the magnetic
disk for a load/unload system, it is possible to prevent occurrence
of an unstable flying condition of the magnetic head due to fly
stiction of the magnetic head which is specific to the load/unload
system, and occurrence of a head crash defect and a thermal
asperity defect resulting therefrom.
[0067] As regards the surface roughness of the texture in case
where the glass substrate is used as the magnetic disk for a
load/unload system, a flat and smooth surface having Rmax of 5 nm
or less and Rp of 2.5 nm or less is preferable in order to improve
a durability of the magnetic disk. In order to further improve the
magnetic characteristic and the durability of the magnetic disk, a
flat and smooth surface having Rp of 2.0 nm or less is
preferable.
BRIEF DESCRIPTION OF THE DRAWING
[0068] FIG. 1A is a side view showing one example of a tape
texturing apparatus.
[0069] FIG. 1B is a perspective view showing the one example of the
tape texturing apparatus.
[0070] FIG. 2 is a view showing a profile of a principal surface of
a magnetic disk obtained in an example of this invention as
observed by an AFM.
[0071] FIG. 3 is a view showing a profile of a principal surface of
a glass substrate for a magnetic disk obtained in a comparative
example as observed by the AFM.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0072] Now, description will be made of embodiments of this
invention in conjunction with specific examples. It is noted here
that this invention is not limited to the following example.
EXAMPLE 1
[0073] A glass substrate for a magnetic disk in this example is a
glass disk substrate for a magnetic disk, which is obtained by
forming a texture by tape polishing on a principal surface of an
amorphous aluminosilicate glass disk substrate chemically
strengthened and thereafter cleaning the principal surface by tape
cleaning.
[0074] Specifically, the glass substrate for a magnetic disk in
this example was produced through (1) a rough lapping step (rough
grinding step), (2) a shaping step, (3) a fine lapping step (fine
grinding step), (4) an end face mirror-polishing step, (5) a
principal surface mirror-polishing step, (6) a chemically
strengthening step, (7) a texturing polishing step, and (8) a tape
cleaning step.
[0075] (1) Rough Lapping Step
[0076] A disk-shaped glass substrate comprising an aluminosilicate
glass and having a diameter of 66 mm.phi. and a thickness of 1.5 mm
was obtained from a molten glass by direct pressing using an upper
die, a lower die, and a body die. The disk-shaped glass substrate
may be obtained by cutting, with a grindstone, a sheet glass formed
by a down drawing method or a floating method instead of the direct
pressing. As the above-mentioned aluminosilicate glass, use was
made of a chemically strengthened glass containing 58-75 wt %
SiO.sub.2, 5-23 wt % Al.sub.2O.sub.3, 3-10 wt % Li.sub.2O, and 4-13
wt % Na.sub.2O. Next, the glass substrate was subjected to a
lapping step for improving a dimensional accuracy and a profile
accuracy. The lapping step was carried out by the use of a
double-sided lapping apparatus and abrasive grains having a
particle size of #400. In detail, opposite surfaces of the glass
substrate received in a carrier were lapped to a surface accuracy
of 0-1 .mu.m and a surface roughness (Rmax) of about 6 .mu.m by
using alumina abrasive grains having a particle size of #400 at
first, setting a load of about 100 kg, and rotating a sun gear and
an internal gear of the lapping apparatus.
[0077] (2) Shaping Step
[0078] Then, a center portion of the glass substrate was bored by
the use of a cylindrical grindstone and an outer peripheral end
face was ground to reduce a diameter to 65 mm.phi.. Thereafter, the
outer peripheral end face and an inner peripheral end face were
subjected to predetermined chamfering. At this time, each end face
of the glass substrate had a surface roughness of about 4 .mu.m in
Rmax. Generally, in a 2.5-inch HDD (hard disk drive), a magnetic
disk having an outer diameter of 65 mm is used.
[0079] (3) Fine Lapping Step
[0080] Next, the abrasive grains were changed into those having a
particle size of #1000 and the surfaces of the glass substrate were
lapped to obtain the surface roughness of about 2 .mu.m in Rmax and
about 0.2 .mu.m in Ra. The glass substrate after the lapping step
was successively dipped into cleaning tanks (applied with
ultrasonic waves) respectively filled with a neutral detergent and
water to be subjected to ultrasonic cleaning.
[0081] (4) End Face Mirror-Polishing Step
[0082] Then, by brush polishing, the end faces (inner peripheral
and outer peripheral) of the glass substrate were polished while
the glass substrate was rotated so that the surface roughness was
equal to about 1 .mu.m in Rmax and about 0.3 .mu.m in Ra. The
surfaces of the glass substrate after the end face mirror polishing
step were cleaned with water.
[0083] (5) Principal Surface Mirror-Polishing Step
[0084] Next, in order to remove a flaw or a distortion left after
the above-mentioned lapping step, a first polishing step was
carried out by the use of a double-sided polishing apparatus. In
the double-sided polishing apparatus, the glass substrate held by a
carrier was interposed between and brought into tight contact with
upper and lower surface tables with polishing pads attached
thereto. The carrier was engaged with a sun gear and an internal
gear. The glass substrate was clamped and pressed by the upper and
the lower surface tables. Thereafter, a polishing liquid was
supplied between the polishing pads and polished surfaces of the
glass substrate and rotation was started. Consequently, the glass
substrate was rotated and revolved on the surface tables so that
the opposite surfaces were simultaneously polished. Hereinafter,
the same apparatus was used as the double-sided polishing apparatus
used in each specific example. In detail, the polishing step was
performed by the use of a hard polisher (hard foamed urethane) as a
polisher. As a polishing condition, the polishing liquid was RO
water with cerium oxide (average particle size of 1.3 .mu.m)
dispersed therein as an abrasive, the load was equal to 100
g/cm.sup.2, and the polishing time was 15 minutes. The glass
substrate after the above-mentioned first polishing step was
successively dipped into cleaning tanks respectively filled with a
neutral detergent, pure water, pure water, IPA (isopropyl alcohol),
and IPA (vapor dry) to be subjected to ultrasonic cleaning and then
dried.
[0085] Next, by the use of a double-sided polishing apparatus of
the type same as that used in the first polishing step mentioned
above, a second polishing step was carried out after changing the
polisher into a polishing pad of a soft polisher (suede). The
second polishing step was mirror polishing intended to polish the
principal surface of the glass substrate into a flat and smooth
mirror-finished surface having a surface roughness of about 8 nm or
less in Rmax while maintaining a flat surface obtained in the first
polishing step mentioned above. As a polishing condition, a
polishing liquid was RO water with cerium oxide (average particle
size of 0.8 .mu.m) dispersed therein, the load was equal to 100
g/cm.sup.2, and the polishing time was 5 minutes. The glass
substrate after the above-mentioned second polishing step was
successively dipped into cleaning tanks respectively filled with a
neutral detergent, pure water, pure water, IPA, and IPA (vapor dry)
to be subjected to ultrasonic cleaning and then dried.
[0086] (6) Chemically Strengthening Step
[0087] Next, the glass substrate after the above-mentioned cleaning
was chemically strengthened. The chemically strengthening step was
carried out by preparing a chemically strengthening solution
comprising a mixture of potassium nitrate and sodium nitrate,
heating the chemically strengthening solution to 380.degree. C.,
and dipping the glass substrate after cleaned and dried into the
chemically strengthening solution for about 4 hours. The glass
substrate after chemically strengthened was successively dipped
into cleaning tanks respectively filled with sulfuric acid, a
neutral detergent, pure water, pure water, and IPA, IPA (vapor dry)
to be subjected to ultrasonic cleaning and then dried.
[0088] Then, the surface of the glass substrate after the
above-mentioned cleaning was subjected to visual inspection and
precise examination utilizing reflection, scattering, and
transmission of light. As a result, no defect such as protrusions
formed by adhered matters or flaws was found out on the surface of
the glass substrate. Further, the surface roughness of the
principal surface of the glass substrate obtained via the
above-mentioned steps was measured by an atomic force microscope
(AFM). As a result, the glass substrate for a magnetic disk having
an ultra smooth surface having Rmax of 2.13 nm and Ra of 0.20 nm
was obtained. The glass substrate had an outer diameter of 65 mm,
an inner diameter of 20 mm, and a thickness of 0.635 mm.
[0089] (7) Texturing Polishing Step
[0090] By the use of the above-mentioned single-substrate rotary
tape texturing apparatus illustrated in FIG. 1, polishing and
circumferential texturing were carried out.
[0091] As a tape, a polyester fiber fabric tape was used. As a hard
abrasive, a slurry containing polycrystalline diamond having an
average particle size of 0.125 .mu.m dispersed in a dispersive
agent was used.
[0092] A texturing polishing condition was as follows.
1 Working Pressure 10 g/mm.sup.2 Substrate Rotation Speed 150 rpm
Tape Feeding Speed 3 mm/sec Texturing Time 50 seconds
[0093] (8) Tape Cleaning Step
[0094] After a circumferential texture was formed on the principal
surface of the glass substrate, the principal surface was subjected
to tape cleaning.
[0095] Specifically, in an apparatus similar to the
single-substrate rotary tape texturing cleaning tape apparatus used
in the texturing polishing step mentioned above, a tape having a
foamed polyurethane surface with a surface pore size of 40 .mu.m in
average was used and DI water comprising neutral ultra pure water
was supplied instead of the polishing slurry. By such a
single-substrate rotary tape cleaning apparatus having the
above-mentioned structure, the principal surface of the glass
substrate provided with the texture was rubbed and cleaned.
[0096] The pressure, the substrate rotation speed, the tape feeding
speed, and the processing time in tape cleaning were similar to
those in the texturing polishing step.
[0097] After the tape cleaning, the glass substrate was subjected
to scrub cleaning by the use of a scrub pad. As a cleaning liquid,
an alkaline cleaning liquid of PH 8 was used.
[0098] Next, the glass substrate for a magnetic disk obtained in
this example was subjected to a deposition step mentioned below to
obtain a magnetic disk.
[0099] By the use of a single-substrate sputtering apparatus, a
seed layer, an underlying layer, a magnetic layer, a protection
layer, and a lubrication layer were successively formed on the
glass substrate provided with the texture.
[0100] As the seed layer, a first seed layer comprising a CrTi thin
film (thickness 300 angstroms) and a second seed layer comprising
an AlRu thin film (thickness: 400 angstroms) were formed. The
underlying layer comprising a CrW thin film (thickness: 100
angstroms) was provided so as to improve a crystal structure of the
magnetic layer. The CrW thin film has a composition of Cr: 90 at %
and W: 10 at %.
[0101] The magnetic layer comprises a CoPtCrB alloy and has a
thickness of 200 angstroms. In the magnetic layer, the contents of
Co, Pt, Cr, and B are Co: 73 at %, Pt: 7 at %, Cr: 18 at %, and B:
2 at %.
[0102] The protection layer serves to prevent the magnetic layer
from being deteriorated by contact with a magnetic head and
comprises hydrogenated carbon having a thickness of 50 angstroms,
providing wear resistance. The lubrication layer is formed by
applying a perfluoropolyether liquid lubricant by dipping and has a
thickness of 9 angstroms.
[0103] A fine profile of a principal surface of the magnetic disk
thus obtained was observed in detail by the use of an AFM (atomic
force microscope). As a result, a circumferential texture along a
circumferential direction of the disk was observed. FIG. 2 shows a
texture profile thereof. An observed region in FIG. 2 is a region
of 5 .mu.m.times.5 .mu.m on the principal surface of the magnetic
disk. Herein, the disturbance in texture profile as seen from FIG.
3 mentioned above was not observed.
[0104] The surface roughness of the texture obtained from the
result of observation by the AFM was 4.57 nm in Rmax and 1.89 nm in
Rp.
[0105] Next, the magnetic disk thus obtained was evaluated as
follows.
[0106] [Evaluation of Magnetic Characteristic]
[0107] The magnetic characteristic was measured by VSM (vibrating
sample magnetometry). A circular sample having a diameter of 8 mm
was cut from the magnetic disk around a position of 22 mm in radius
as a center. An external magnetic field was applied (.+-.10 kOe) in
each of a circumferential direction and a radial direction of the
substrate to obtain a magnetization curve. Mrt (residual
magnetization-thickness product) in the circumferential direction
of the substrate and Mrt in the radial direction were calculated.
As a result, the ratio of Mrt in the circumferential direction with
respect to Mrt in the radial direction (magnetic anisotropy) was
equal to 1.33.
[0108] [Evaluation of Reliability]
[0109] The magnetic disk thus obtained was evaluated for a glide
characteristic. As a result, a touch down height was equal to 4.5
nm. The touch down height is a measure of an ability of the
magnetic disk for a flying height by successively lowering the
flying height of a flying head (for example, lowering the rotation
speed of the magnetic head) and obtaining a particular flying
height at which the head is first contacted with the magnetic disk.
Generally, in a HDD required to have a recording density of 40
Gbit/in.sup.2 or more, the touch down height must be equal to 5 nm
or less.
[0110] Further, LUL durability was tested by repeatedly carrying
out load/unload operations of the head at a flying height of 12 nm
during flight of the head and under the environment of 70.degree.
C. and 80% RH. As a result, no head crash defect occurred even
after the test of consecutive 600,000 times of LUL operations. It
is said that, in a HDD generally used, about ten years of use will
be required until the number of times of LUL operations exceeds
600,000. By the use of a GMR head having a flying height of 12 nm,
a thermal asperity (TA) test was carried out. As a result, no
thermal asperity defect occurred.
[0111] A surface of the magnetic head after the load/unload test
mentioned above was observed by an optical microscope. As a result,
no contamination was observed.
EXAMPLE 2
[0112] In this example, a glass substrate for a magnetic disk was
produced by a production method similar to that in Example 1 except
that the tape used in (8) Tape Cleaning Step in Example 1 was
replaced by a tape having a polyester surface similar to the tape
used in the texturing polishing step. Further, by the use of the
glass substrate, a magnetic disk was produced in the manner similar
to Example 1.
[0113] A fine profile of a principal surface of the magnetic disk
thus obtained was observed in detail by the AFM. As a result, a
circumferential texture along a circumferential direction of the
disk was observed like in FIG. 2. The surface roughness of the
texture was obtained from the result of observation by the AFM and
was equal to 4.96 nm in Rmax and 2.98 nm in Rp which were slightly
greater as compared with Example 1.
[0114] The magnetic characteristic of the magnetic disk thus
obtained was evaluated in the manner similar to Example 1. As a
result, the oriented ratio was equal to 1.32.
[0115] Further, the glide characteristic was evaluated. As a
result, the touch down height was equal to 4.8 nm.
[0116] The LUL durability was tested also. As a result, no head
crash defect occurred even after a test of consecutive 600,000
times of LUL operations. A thermal asperity test was carried out.
As a result, no thermal asperity defect occurred.
[0117] On a surface of the magnetic head after the load/unload
test, adhesion of a very small amount of contamination was
observed.
EXAMPLE 3
[0118] In this example, the treating liquid used in (8) Tape
Cleaning Step in Example 1 contained colloidal silica particles
(concentration of 22 wt %) as colloidal particles. The colloidal
silica particles had an average particle size of 0.15 .mu.m. The
treating liquid was adjusted to be alkaline with PH 10 by addition
of sodium hydroxide (NaOH).
[0119] A glass substrate for a magnetic disk was produced by a
production method similar to that in Example 1 except the
above-mentioned respects. Further, by the use of the glass
substrate, a magnetic disk was produced in the manner similar to
Example 1.
[0120] A fine profile of a principal surface of the magnetic disk
thus obtained was observed in detail by the use of the AFM. As a
result, a circumferential texture along a circumferential direction
of the disk was observed like in Example 1.
[0121] The magnetic characteristic of the magnetic disk thus
obtained was evaluated in the manner similar to Example 1. As a
result, the oriented ratio was 1.33.
[0122] The glide characteristic was evaluated. As a result, an
excellent characteristic represented by the touch down height of
4.2 nm was obtained.
[0123] Further, the LUL durability was tested. As a result, no head
crash defect occurred even after a test of consecutive 600,000
times of LUL operations. The thermal asperity test was carried out.
As a result, no thermal asperity defect occurred.
[0124] A surface of a magnetic head after the load/unload test was
observed by the optical microscope. As a result, no contamination
was observed.
EXAMPLE 4
[0125] In Example 4, a glass substrate for a magnetic disk was
produced by a production method similar to that in Example 1 except
that the scrub cleaning carried out in (8) Tape Cleaning Step in
Example 1 by using the scrub pad after the tape cleaning was not
carried out. Further, by the use of the glass substrate, a magnetic
disk was produced in the manner similar to Example 1.
[0126] A fine profile of a principal surface of the magnetic disk
thus obtained was observed in detail by the use of the AFM. As a
result, a circumferential texture along a circumferential direction
of the disk was observed like in Example 1. The surface roughness
of the texture obtained from the result of observation by the AFM
was 4.59 nm in Rmax and 1.85 nm in Rp. These values were
substantially similar to those in Example 1.
[0127] The magnetic characteristic of the magnetic disk thus
obtained was evaluated in the manner similar to Example 1. As a
result, the oriented ratio was equal to 1.33.
[0128] Further, the glide characteristic was evaluated. As a
result, the touch down height was equal to 4.8 nm.
[0129] The LUL durability was tested also. As a result, no head
crash defect occurred even after a test of consecutive 600,000
times of LUL operations. The thermal asperity test was carried out.
As a result, no thermal asperity defect occurred.
[0130] A surface of a magnetic head after the load/unload test was
observed by the optical microscope. As a result, no contamination
was observed.
COMPARATIVE EXAMPLE 1
[0131] A glass substrate for a magnetic disk was produced by a
production method similar to that in Example 1 except that (8) Tape
Cleaning Step in Example 1 was not carried out. Further, by the use
of the glass substrate, a magnetic disk was produced in the manner
similar to Example 1.
[0132] A fine profile of a principal surface of the magnetic disk
thus obtained was observed by the use of the AFM. As a result, a
circumferential texture was observed. However, disturbance
resulting from a texture profile on the surface of the glass
substrate was observed as seen from FIG. 3 mentioned above. The
surface roughness of the texture was 5.18 nm in Rmax and 3.30 nm in
Rp. As compared with Example 1, Rp was degraded by 1.41 nm. This is
because the texture profile was disturbed by a streak of texture
higher than a surrounding texture profile like the one observed at
a lower right portion in FIG. 3.
[0133] The magnetic characteristic of the magnetic disk thus
obtained was evaluated in the manner similar to Example 1. As a
result, the oriented ratio was equal to 1.32.
[0134] Further, the glide characteristic was evaluated. As a
result, the touch down height was equal to 5.4 nm. The LUL
durability was tested also. As a result, a failure occurred by head
crash after 400,000 times of LUL operations. The thermal asperity
test was carried out. As a result, a thermal asperity defect
occurred also. On a surface of a magnetic head after the
above-mentioned load/unload test, adhesion of contamination was
observed.
EXAMPLE 5
[0135] The tape used in (8) Tape Cleaning Step in Example 1 was
replaced by a pile tape (trade name: SPD2501-NF). By the use of a
glass substrate obtained, a magnetic disk was produced in the
manner similar to Example 1.
[0136] A fine profile of a principal surface of the magnetic disk
thus obtained was observed by the use of the AFM. As a result, a
circumferential texture was observed. However, disturbance
resulting from a texture profile on the surface of the glass
substrate was observed as seen from FIG. 3 mentioned above. The
surface roughness of the texture was 5. 02 nm in Rmax and 2.88 nm
in Rp. As compared with Example 1, Rp was degraded. This is because
the texture profile was disturbed by a streak of texture higher
than a surrounding texture profile like the one observed at the
lower right portion in FIG. 3.
[0137] The magnetic characteristic of the magnetic disk thus
obtained was evaluated in the manner similar to Example 1. As a
result, the oriented ratio was equal to 1.32.
[0138] Further, the glide characteristic was evaluated. As a
result, the touch down height was equal to 4.9 nm. The LUL
durability was tested also. As a result, a failure occurred by head
crash after 400,000 times of LUL operations. The thermal asperity
test was carried out. As a result, a thermal asperity defect
occurred also. On a surface of a magnetic head after the
above-mentioned load/unload test, adhesion of contamination was
observed.
[0139] As described above in detail, in the method of producing a
glass substrate for a magnetic disk according to this invention,
the texture is formed on the principal surface of the glass
substrate and thereafter the cleaning with the tape is carried out
while supplying the treating liquid onto the principal surface.
Thus, foreign matters and the like adhered to the principal surface
of the substrate after forming the texture can be removed and the
disturbance in texture profile is suppressed so as to form a
uniform texture.
[0140] By producing a magnetic disk using the glass substrate for a
magnetic disk according to this invention, it is possible to
provide a magnetic disk which is capable of suppressing adhesion of
contamination onto a magnetic head and preventing occurrence of a
head crash defect and a thermal asperity defect against a reduction
in flying height and which is high in reliability and suitable for
a higher recording density.
* * * * *